Exam Question
(a) Draw circuit diagram and explain working of star/delta starter. (8)
(b) Explain with diagram how direction of single phase induction motor is reversed. (8)
ETO
ETO Exam papers
📅 Nov 2025
Reference Answer
(a)
In operation, the main contactor and the star contactor are closed initially and then after a period of time, the star contactor is opened, and then the delta contactor is closed. The control of the contractors is by the timer built into the starter. The star and delta are electrically interlocked and preferably mechanically interlocked as well. The control circuit is provided with a manual stop button and a thermal overload contact to shut down the motor.
In operation, the main contactor and the star contactor are closed initially and then after a period of time, the star contactor is opened, and then the delta contactor is closed. The control of the contractors is by the timer built into the starter. The star and delta are electrically interlocked and preferably mechanically interlocked as well. The control circuit is provided with a manual stop button and a thermal overload contact to shut down the motor.
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